Amplifier



Aug. 20, 1940. EPP' 2,212,204

AMPLIFIER Filed Jan. 4, 1939 2 Sheets-Sheet l INVENTOR GERA RDv H PPWf/L/ ATTORNEY Aug. 20, 1940. HEPP 2,212,204

AMPLIFIER Filed Jan. 4, 1939 2 Sheets-Sheet 2 INVENTOR GERARD HEPP BYj-kgg ATTORNEY Patented Aug.. 20, 1940 UNITED STATES PATENT AMPLIFIERDelaware Application January 4, 1939, Serial No. 249,221 In GermanyJanuary 4, 1938 5 Claims.

. This invention relates to amplifying arrangements particularly adaptedfor uniform amplification of broad frequency bands including Very lowfrequencies.

Wide band amplifiers having uniform amplification orfrequency-independent characteristics are of considerable importance inelectrical arts, and especially in television. Hitherto, theconstruction of such amplifiers have been exceedingly dimcult and costlyand, in many cases, could only provide uniform amplification at the costof non-uniform time delay of signals of different frequency known asnon-linear phase response characteristic. This invention provides arelatively simple and cheap means of obtaining uniform amplificationthrough a wide band of frequencies and at the same time preservinguniform phase response.

Accordingly, it is an object of this invention to provide an improvedwide band amplifier.

Another object of the invention is to provide a simple wide bandamplifier having uniform amplification and time delay.

Other objects of my invention Will become apparent upon reading thedetailed description, together with the drawings.

In the drawings,

Fig. 1 schematically shows a single stage amplifier having embodiedtherein impedances chosen in accordance with my invention,

Figs. 2, 3, 5 and 6 show modifications of the embodiment in Fig. 1 inmore detail and structural elements shown in Fig. 1; while Fig. 4 showsa circuit arrangement for reducing the efiect of the stray capacity of alarge condenser. I

As is well known, the frequency dependency of an amplifier is first ofall determined by the frequency dependency of the coupling meansprovided between the individual amplifying stages, such as the impedanceZ8. in the anode circuit of an amplifying tube, the impedance Z2 in thegrid circuit of the succeeding tube and the coupling impedance Z1between the anode circuit and the grid circuit. Furthermore, thefrequency-dependency of an amplifier, more particularly at lowfrequencies, is materially afiected by the impedance Zk which isinserted in the cathode lead for obtaininga suitable grid bias and whichusually comprises a resistance and a condenser connected. in paralleltherewith. When using tubes having a plurality of grids, the screengridlead may further include an impedance ZS which serves for smoothing thescreen-grid voltage and the common lead of anode and screen grid maycomprise an impedance Z (such as the internal impedance of the source ofanode voltage). These impedances, also, affect the frequency-dependencyof the amplifier.

Considering all of the above mentioned impedances, we obtain the diagramof connections of an amplifying stage represented in Fig. 1.

The present invention allows by means of such a circuit arrangement,which includes one or more frequency-dependent impedances, to obtain afrequency-independent amplification i. e. a frequency-independent ratiobetween the voltage 62 set up between the' output terminals A1A2 and thevoltage 61 set up between the input terminals E1, E2.

The amplifier may comprise a plurality of am- I plifying stages of thetype illustrated in Fig. 1,

in which case the invention allows not only of rendering each individualstage frequency-independent, but also to compensate in one stage thefrequency-dependency of another stage.

According to the present invention the impedance Za in the anode-circuitand the impedance Z2 between the output terminals of the amplifyingstage consist for this purpose of a resistance in series with impedanceswhich are proportional respectively to the impedance Zk in the cathodelead, to the impedance 25 in the screen-grid lead, to the impedance Zcin the common anodeand screen-grid lead, which impedances form part ofthe said amplifying stage and/or of another amplifying stage, whereasthe impedance Z... furthermore comprises impedances proportional to thecoupling impedance Z1 in the said amplifying stage and/or in anotheramplifying stage.

The arrangement of an amplifying stage according to the invention isrepresented in Fig. 2. As appears therefrom, the anode impedance Zaconsists of a resistance Ra in series with impedances ZS, flZc, 'yZk and5Z1 which are proportional to the impedances ZS, Zc, Zr and Z1respectively, whereas the impedance Z2 between the output terminals A1and A2 consists of a resistance in series with impedances Theproportionality factors a, c, 'y and 8 must be chosen so as to fulfillthe following conditions.

cc Raqss fi =(1+q) (RaSs-1) y =Ra(SI-Ss) (1+q) 6 =any positive ValueEE=Ra( +q) Ss wherein: 1

q is the ratio between the screen grid, alternating current s and theanode alternating current ia, which ratio may be considered to beconstant,

SS is the mutual conductance of the characteristic curve of the anodecurrent/screen-grid voltage, and

S is the mutual conductance of the characteristic curve of the anodecurrent/control-grid voltage.

When these conditions are observed the amplification amounts to 2 e1SRaand this is consequently frequency-independent. The iinpedances Z5, Zand Z1; may, for instance comprise resistances Rs, Re, Rk together withparallel condensers Cs, Cc and Ck as shown in Fig. 3'. The impedancesZS, 5Z0 and "YZk in the anode circuit must then comprise resistancesozRs, [3R0 and 'yRk together with parallel condensers and In the samemanner the imp-edances 5 i i 6 7 5 Z and 6 J];

between the output terminals A1 and A2 are constituted by the parallelconnections of resistances a c l R 5R and R and condensers 6 6 i C, and(J,, or e y In Fig. 3, the coupling impedance comprises a condenser C1.A condenser proportional thereto must consequently be interposed in theanode circuit. However, this blocks the direct current of the anode andmust consequently be bridged by a resistance 631. Since,

on the one hand, this resistance may not be given a high value onaccount of the excessive voltage drop, which otherwise would be causedby the anode current and may, on the other hand, not be too small, sinceotherwise amplification of the low frequencies would depend on passesdirect current.

the frequency, a resistance R1 is, according to This condenser 0 musthave a sufficient capacity so that its impedance may be neglected withrespect to the resistance R1 even with the lowest frequencies to beamplified. To avoid that the considerable capacity with respect to earthof such a large condenser may affect the amplification of the highfrequencies the resistance R1 is -preferably divided into two'par ts Rbetween which the condenser C is connected as shown in Fig. 4.

The proportionality factor B=(1+q) (Russ-1) may become negative if Ra Ss1, which would involve a negative impedance ,BZc in the anode circuit,which cannot be realized in most cases.

Then it is advantageous to make use of the circuit arrangements shown inFig. 5 or 6.

The circuit arrangement shown in Fig. 5 may be deduced in the followingmanner from the circuit arrangement shown in Fig. 2. When interposing inthe latter an impedance in series with Z1 a proportional impedance(l-l-q)Zc must be interposed in the anode circuit. Together with theimpedance 52 a positive impedance.

then results.

In Fig. 6, the impedance which is positive for negative 5 is connectedin series with Z1; in this case the impedance proportional to Z0 in theanode circuit may be entirely omitted.

It will be appreciated that the invention may also be used in amplifiersin which one or more of the impedances Zk, Z5 and Z0 are equal to zero.Of course, the impedances proportional thereto, which are included in Zaand Z2, are then also equal to zero.

Furthermore, it is possible in an amplifying stage to compensate inanother amplifying stage the influence of one or more of the impedancesZk, Zs, Z'c and Z1 included in the first-mentioned amplifying stage, byinterposing in the impedances Z3. and Z2 of this other stage impedancesproportional to Zk, Zs and Zc. In

this case, the proportionality factors a, 5, 'y, 5'

must, of course be chosen in accordance with the particularities of thetubes and circuit arrangements in use.

What is claimed is:

l. A wide band amplifier having uniform amplification comprising anelectron discharge tube having a cathode, control electrode, screen gridand anode, a voltage supply source, a common lead, a first impedanceconnected between said cathode and common lead, a second impedanceconnected between said screen grid and a third impedance, said thirdimpedance being connected to the common lead through the supply source,a coupling impedance connected between the anode and a first outputterminal, a second output terminal connected to the common lead, ananode circuit comprising a first resistor, a fourth impedanceproportional to said second impedance, a fifth impedance proportional tosaid third impedance, a sixth impedance proportional to said first and aseventh impedance proportional to said coupling impedance, said resistorand fourth, fifth, sixth and seventh impedances being serially connectedbetween the anode and said third impedance, and a second resistorconnected in series with a plurality of impedances proportionalrespectively to said first second and third impedances, said secondresistor and plurality of impedances being connected across the firstand second terminals.

2. An amplifier as claimed in claim 1 and wherein each of the namedimpedances comprises a parallelly connected resistance and capacity.

3. An amplifier as claimed in claim 1 and wherein the said couplingimpedance comprises connected in series in the order named a firstresistor element, a first condenser element, and a second resistorelement, and a second condenser connected across the serially connectedelements.

4. An amplifier as claimed in claim 1 and comprising in addition afurther impedance proportional to the third impedance, said furtherimpedance being connected in series with said coupling impedance and tosaid anode.

5. A wide band amplifier having uniform amplification comprising anelectron discharge tube having a cathode, control electrode, screen gridand anode, a voltage supply source, a common lead, a first impedanceconnected between said cathode and common lead, a second impedanceconnected between said screen grid and a third impedance, said thirdimpedance being connected to the common lead through the supply source,a coupling impedance connected between the anode and a first outputterminal, a second output terminal connected to the common lead, ananode circuit comprising a first resistor, a fourth impedanceproportional to said second impedance, a fifth impedance proportional tosaid third impedance, a sixth impedance proportional to said first and aseventh impedance proportional to said coupling impedance, said resistorand fourth, fifth, sixth and seventh impedances being serially connectedbetween the anode and third impedance, a second resistor connected inseries with a plurality of impedances proportional respectively to saidfirst, second and third impedances, said second resistor and pluralityof impedances being connected across the first and second terminals, andterminal means to impress control voltage between said control electrodeand said common lead.

GERARD HEPP.

